1. Field of the Invention
The present invention relates to a technology for improving the quality of images formed using an electrophotography process.
2. Description of the Related Art
A typical known image forming apparatus that uses an electrophotography process causes an oscillating or rotating laser scanner to reflect a light beam modulated by a pixel signal onto a rotating photosensitive body to form an electrostatic latent image. In such an image forming apparatus, movement fluctuations of each movable component can distort an image to be formed. For example, speed fluctuations of an image bearing member cause color misregistration.
Japanese Patent Laid-Open No. 2005-181655, for example, discloses an image forming apparatus that reduces color misregistration caused by speed fluctuations of an image bearing member. More specifically, the image forming apparatus detects the rotational speed of an intermediate transfer belt and performs an interpolation process for adding scanning lines or a decimation process for reducing scanning lines.
However, when image forming apparatuses use devices whose scanning frequency can vary or change as laser scanners, the sub-scanning width (the distance between two adjacent main scanning lines) can vary among the image forming apparatuses. When micro electromechanical system (MEMS) scanners, which are small and low-priced oscillating devices, are used as the laser scanners, the scanning frequency may vary among the MEMS scanners and may change with the passage of time. Although it is technically possible to perform feedback control on the MEMS scanners having natural frequencies to correct their scanning frequency, it involves high cost.
Accordingly, in an image forming apparatus that uses a plurality of MEMS scanners corresponding to colors, variation in scanning frequency among the MEMS scanners causes variation in sub-scanning width among the colors, i.e., color misregistration, on a sheet of transfer material. This makes it difficult to obtain a high-quality full color image.